Although there have been a great number of studies evaluating the personality and emotional characteristics of temporomandibular joint (TMJ) dysfunction syndrome and myofascial pain dysfunction (MPD) syndrome patients, the exact nature of the associations are still unclear. A primary reason for this is the absence of a uniform and reliable diagnostic system and nomenclature used across studies to classify patients with chronic pain. The major purpose of the present proposed study is to employ the DSM-III-R multiaxial classification criteria, derived on the basis of a new structured interview format, for classifying TMJ-MPD patients. Five separate groups of subjects will be evaluated: (1) Acute TMJ-MPD patients; (2) Chronic TMJ-MPD patients; (3) Acute low back pain patients; (4) Chronic low back pain patients; (5) Normal pain-free subjects. Besides establishing the incidence of DSM-III-R disorders in these groups, this design will also address three other important issues. First, are there any associations between specific DSM-III-R diagnostic categories and the presence or absence of specific pathophysiological findings? Secondly, are there differences in the psychological-personality category profiles of acute versus chronic patients? Finally, are there unique patterns of psychological-personality disorders associated with specific types and sites of pain (TMJ-MPD versus low back) or are the patterns similar in terms of DSM-III-R diagnoses? This more precise and standard classification of psychological and medical diagnoses of these patients will significantly aid in expanding our knowledge of these syndromes, as well as developing more effective treatment strategies for dealing with the psychological and personality variables associated with them.